Within the context of high resolution imaging methods, such as for example in computer tomography in medical imaging, generally X-ray detectors are used in order to produce a three-dimensional image with a high resolution of an area of a patient to be examined.
An X-ray detector, the sensor layer thereof being configured as a directly converting semi-conductor layer, permits in this case a quantitative and energy-selective detection of individual X-ray quanta. With the incidence of X-ray radiation, electron hole pairs, i.e. pairs of negative and positive charge carriers, are produced in the sensor layer. By way of a voltage applied to the sensor layer and/or to the surface of the sensor layer, the charge carriers are separated and move toward the respective opposingly charged electrodes and/or surfaces of the sensor layer. The current thereby produced or a corresponding charge transfer may be evaluated by an electronic sensor unit connected downstream. For example semi-conductor materials in the form of CdTe, CdZnTe, CdTeSe, CdZnTeSe, CdMnTe, GaAs, Si or Ge which have a high absorption cross section for X-ray radiation are suitable for detecting the X-ray quanta.
Large-surface X-ray detectors are required, in particular, in computer tomography and to this end a plurality of relatively small detector modules are frequently arranged adjacent to one another. Such detector modules in turn consist of individual sensor boards which are arranged adjacent to one another with the smallest possible spacing (˜100 μm) on a common carrier, the sensor layers thereof together forming the sensor surface of a detector module.
During the production of a sensor board it is usual to arrange a reader unit, such as for example an ASIC, in a stacked construction initially on a sensor layer and subsequently to fix the components to one another. This stacked construction is denoted as a hybrid.
Flip-chip technologies which are common in connection techniques may be used for producing a sensor board, small subassemblies being able to be manufactured rapidly thereby in a tightly packed manner. Here, the respective components to be connected to form a subassembly, i.e. in the present case the reader unit and the sensor layer, may be fixed together by way of an adhesive bonding method, for example.
Alternatively, fixing may take place by way of a soldering method. To this end, generally soldering elements from a low-melting solder material are used as contact or connecting elements (“bumps”) by which the components to be connected are fastened together. In the production of a hybrid, such soldering elements are applied to the surface of the reader unit facing the sensor layer in the integrated state and the reader unit is then brought into contact with the sensor layer via the soldering elements. By a subsequent heating of the solder material which is generally carried out by specific temperature adjustment of the mounting tools used for positioning the components, the components are connected together. This is referred to as so-called reflow soldering. When producing a hybrid, at least two method steps have to be carried out for each reader unit to be fixed. This is a drawback in the case of a plurality of reader units for each sensor layer.